Field of Invention
The present invention relates to a motor control, and more particularly to a flyback control mode-based controller and the motor-controlling method thereof.
Description of Related Arts
The operating principle for a power supplying system is that the power supplying system outputs power is defined as a forward control mode. Then, the power supplying system utilizing the stored energy as an output when the power source is switched off is defined as the “flyback” control mode.
Accordingly, the existing electromechanical device comprises an electrical system, a mechanical system, and a magnetic system that generates a magnetic field to magnetically link the electrical system with the mechanical system. According to the conservation of energy principle, electrical energy generated by the power input=the increase of stored energy in the magnetic field+the energy loss in the system+the mechanical energy output. Under the lossless conditions, i.e. ignoring the energy loss, the equation of the energy transfer is that: dWf=dWe+dWm, where dWe is the differential electric-energy input, dWf is the differential change in magnetic stored energy, and dWm is the differential mechanical energy output. For the existing motor assembly, the stored energy in the magnetic field cannot be transformed into mechanical energy. During the phase shift, the remaining energy will be discharged to produce a negative torque. In traditional computing theory, this discharged energy will also be omitted or ignored.
The working mode of the existing motor assembly is the forward control mode, wherein during the ascending current phase, a working cycle of a three-phase motor is ⅓, such that the motor assembly generates the output when increasing the current in each cycle. In particular, the motor assembly can provide motoring as the positive torque when inputting power and can provide negative torque when releasing power.
FIG. 2 illustrates the power circuit of the motor assembly through the current chopping process. There are two different types, i.e. a single diode mode and a double diode mode, and their operations are slightly different. FIG. 2 illustrates the power circuit of the motor assembly with the double diode mode. The advantages of the double diode mode are that the discharge is rapid and energy can be stored through the feedback power from the two diodes. Therefore, the double diode mode is suitable for higher speed application (please see FIG. 3 that illustrates the descending current waveform). On the other hand, the energy cannot be stored through the feedback power in the single diode mode, wherein the energy saved at the diode will be discharged until it is used up. During the motor current chopping process, the work of the motor assembly is provided by the ascending current when the input current is increasing to reach the chopping threshold. Once the input current reaches the chopping threshold, there will be no work for the motor assembly by cutting off the power supply. Once the motor current chopping process is completed, the motor assembly will re-connect to the power supply. For the switch on-and-off of the reluctance motor, its forward control mode is that when the yoke pole of the rotor is aligned with one particular yoke pole of the stator, the corresponding phase coil winding is cut off and the preceding phase coil winding at the rotational direction is then connected. As shown in FIG. 1, when the motor assembly generates a counter-clockwise output, the solenoid coil is initially energized to determine its location. Then, other solenoid coils are energized in sequent at the rotation direction. Therefore, by determining the locations of the solenoid coils, a detection signal can be generated to sequentially connect and disconnect the corresponding solenoid coils. For example, the winding A is electrically connected when the photoelectric signal a is generated. The winding B is electrically connected and the winding A is electrically disconnected when the photoelectric signal b is generated.
According to the forward control mode, during the current chopping process, the current is gradually reduced from its maximum value, wherein there is no work provided by the motor assembly. When the power is cut off, the current is also gradually reduced from its maximum value. At the same time, the phase of current is changing that the corresponding winding is initially connected and is insufficient to generate enough power to overcome the negative torque from the preceding winding. As a result, the motor assembly will be operated in an idle condition. Only when the positive torque generated by the corresponding winding is larger than the negative torque generated by the preceding winding, the motor assembly will continue to generate the rotational power. This is the same reason of the presence of torque pulsations, i.e. torque ripple for the reluctance motor.